1. Field of the Invention
The present invention relates generally to toner used for developing an electrostatic latent image in an image forming apparatus such as a copying machine or a printer, and more particularly, to toner in which fine particles for surface treatment such as a charge-controlling agent are fixed and/or film-formed on the surface of core particles mainly composed of thermoplastic resin.
2. Description of the Prior Art
In an image forming apparatus such as a copying machine or a printer, a variety of types of toner have been conventionally used in developing an electrostatic latent image formed on a photosensitive member.
In recent years, it has been desired to enhance the image quality of an image formed by the above-mentioned image forming apparatus. Correspondingly, it has been positively considered that toner having a small particle diameter is used.
When the toner having a small particle diameter is thus produced, it is difficult to uniformly disperse additives such as a charge-controlling agent in its toner particles, so that the additives are contained in the toner particles in an unevenly dispersed state. As a result, the chargeability or the like of the toner becomes unstable. When an image is formed using the toner, the following problems arise. For example, the image formed is fogged, and the toner is scattered from a developing device to contaminate the inside of the image forming apparatus by the toner.
In recent years, therefore, toner has been produced by fixing or film-forming fine particles for surface treatment such as a colorant or a charge-controlling agent on the surface of core particles by mechanical energy or heat energy mainly comprising an impact force.
However, a kind of charge-controlling agent is not fastened to the surface of the core particles in a uniformly dispersed state, so that the charge-controlling agent may adhere to the surface of the core particles in an unevenly dispersed state, and the charge-controlling agent may be separated from the surface of the core particles to gregate.
As a result, the toner produced in the above described manner varies in composition and characteristics. Particularly, the toner greatly varies in charge controllability, so that the chargeability or the like of the toner is still unstable. When an image is formed using the toner, the following problems still exist. For example, the image formed is fogged to lower the image quality thereof, and the toner is scattered to contaminate the inside of the image forming apparatus by the toner.